JBIDE-17849 CSS Hyperlinks aren't working on non-WTP projects

An utility helper method is added due to find pages in projects that are not the WTP ones
(has no web-roots that can be achieved by WTP methods)

Signed-off-by: vrubezhny <vrubezhny@exadel.com>
This code is taken from org.jboss.tools.jst.web.ui.internal.text.ext.hyperlink.internal.CreateNewFileHyperlinkDetector.getLinkFile(IFile, String), where it's working pretty fine. At least no bugs are reported against it.
I'll double check it.